Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$22.96	3.552%	$23.7755	$23.78	$23.80	$23.80
Purchase #2	$60.66	8.555%	$65.8495	$65.85	$65.85	$65.80
Purchase #3	$78.82	5.460%	$83.1236	$83.12	$83.10	$83.10
Purchase #4	$232.25	9.862%	$255.1545	$255.15	$255.15	$255.20
Purchase #5	$249.96	4.322%	$260.7633	$260.76	$260.75	$260.80
Purchase #6	$89.54	10.637%	$99.0644	$99.06	$99.05	$99.10
Purchase #7	$41.55	12.227%	$46.6303	$46.63	$46.65	$46.60
7 purchase totals =	$775.74		$834.3611	$834.35	$834.35	$834.40